Hydraulic and electric power are generated in aircraft by power take-offs from propulsion engines during flight and/or an auxiliary power unit (APU). Control of an aircraft is dependent upon the generation of electrical and/or hydraulic power. In the event the propulsion engines are rendered inoperative during flight and emergency power cannot be generated by the APU, control of the aircraft may not be maintained without an emergency power source which generates its power from movement of the aircraft through the air.
For this purpose, ram air turbine engines (RATs) are used to generate emergency power in modern jet aircraft, with the RAT being stored within the fuselage or wing of an aircraft except during deployment for the purpose of generating emergency power. Upon deployment, the RAT pivots from a stowed position within the fuselage or wing to a deployed position which extends downwardly from the aircraft to a position where the air intercepts the turbine blades then turns producing power as a consequence of the velocity of the aircraft moving through the air.
An example of a typical RAT construction is disclosed in, for example, U.S. Pat. No. 3,125,960.
Turbine blades for RATs have been and are currently forged or machined from aluminum; however, to enhance the RAT's performance, there has been a demand for turbine blades having an increased axial length. While it initially may appear that an increase in length would not pose any particular problems, the increased axial length involves increase in weight as well as the imposition of higher loads on the hub of the RAT.
For example, if, following the past and current trend, aluminum blades are used for the RAT, it is necessary to completely redesign the RAT hub thereby increasing the weight as well as the mechanical complexity; however, a redesign is not required if the blades are constructed so as to have a mass moment of inertia equal to or at least substantially equal to existing shorter aluminum blades. In order to obtain the desired mass moment of inertia for the longer blades, it is necessary for the blades to be manufactured from a composite material while at the same time minimizing the manufacturing costs and providing a high reproducibility and enabling inspection of the finished turbine blades.
In, for example, U.S. Pat. No. 3,713,753, a laminate construction for an airfoil wing type member is proposed, with the member being produced by machine winding multiple layers of reinforcing fiber about a foil-like material support layer on a rotatable mandrel, with the laminate construction being cut from the mandrel and shaped to a desired configuration in a mold cavity with the addition of a hardenable resin filler material. Adjacent layers of the fibers are wound to form a diamond shaped pattern, with the pitch angles of the fibers in different layers being varied to accommodate different conditions.
U.S. Pat. No. 4,648,921, also proposes a blade construction including an outer shell of a fiber reinforced plastic which is bonded by way of a bonding adhesive to an aluminum spar extending substantially centrally therewith. The lightweight filler material such as a rigid urethane foam is formed within the voids remaining between the shell and the spar, with a protective metal sheath being subsequently fitted and bonded to the leading edge of the blade by an adhesive bond. The spar is provided with a root portion for facilitating interconnection of the blade to a hub.
Yet another composite blade construction is proposed in, for example, U.S. Pat. No. 4,022,547, wherein the blade is fabricated by laying up and bonding together a plurality of filament laminates, with the filaments of at least a portion of the laminates being skewed in a chordwise direction, forward and aft of a non-radial blade axis so as to form a biased lay-up with the blade center of twist biased forward or aft of the blade radial axis. The filaments may be skewed forward so that no filaments run from the blade leading edge to the blade tip but rather from the blade leading edge to the blade root.
U.S. Pat. No. 3,883,267, also proposes a blade construction made of composite fibrous material, with the blade construction comprising a streamlined or airfoil section arranged around a core. The airfoil section is constituted by a superimposition upon the core of a plurality of superimposed layers of composite fibrous material composed of, for example, a matrix of synthetic resin in which is incorporated a fibrous reinforcement having high grade mechanical characteristics and constituted by fibers or filaments of carbon or boron. The core is made of a metal such as titanium and includes a blade fixing root portion 3a constructed so as to be accommodated in a circumference of a disk or drum.
Yet another composite blade construction is proposed in U.S. Pat. No. 3,762,835, wherein the primary structure of the blade comprises elongated graphite fibers embedded in a polymeric resin matrix forming a filament/resin composite with filaments/resin sheets comprising partially cured polymeric resin having a plurality of graphite filaments embedded therein in a generally equi-spaced parallel relationship, arranged in an area of the blade so as to provide protection against damage caused by foreign objects.
While each of the above proposed blade constructions are somewhat effective in achieving their respective stated objectives, each propose the utilization of continuous fibers and a filament winding or laying process to arrive at the desired blade construction.
In, for example, U.S. Pat. No. 4,834,616, a rotor blade is provided which comprises a composite structure formed by laminating multiple plies or layers to provide high strength or high modulus of elasticity for the rotor blade, with the blade being fabricated with an inner core, a composite thickness of woven material about the core, an outer layer, and a single covering layer. The inner core may be fabricated of a closed cell foam, with the composite thickness being a woven composite, the outer layer being formed of a composite of graphite filaments and epoxy resin matrix, and the covering layer being formed of a single ply of glass filaments with an epoxy resin matrix. A socket of a metallic material is provided with a threaded connection for mounting on the rotor hub, with a retention member being positioned within the socket.
In DE 30 15 208 A1, proposes a plastic blade construction wherein each blade includes a metal core having a central spindle with anchoring profiles projecting therefrom. An outer case of plastic material is built-up around the core and profiled to a desired aerodynamic shape. The core includes a projecting member for enabling an attachment to the hub, and a fine metal wire mesh is embedded in an outer layer of the plastic material.